Three-layer coatings are commonly used to protect the outer surface of metal pipes intended for constructing pipelines for oil or gas. These coatings are made up as follows, starting from the metal surface:                primer: epoxy resin        reactive tie, which reacts with the epoxy        polyethylene, advantageously medium-density or high-density polyethylene.        
The tie described in document WO 99/61246 comprises:                (A) 50 to 100 parts of a polyethylene homopolymer or copolymer of relative density equal to 0.9 or higher;        (B) 0 to 50 parts of a polymer chosen from a polypropylene homopolymer or copolymer (B1), the amount of (A) and (B) being 100 parts and the (A)/(B) blend being grafted by at least 0.5% by weight of a functional monomer. This blend is itself diluted in at least one polyethylene homopolymer or copolymer (C).        
The technical problem is to create a novel tie having a high peel strength at temperatures above 80° C. for preferential use in a pipe coating incorporating structures comprising at least one HDPE or MDPE layer. The tie must also be sufficiently fluid to facilitate its processing with a level of grafting <0.5%, preferably less than <0.4%, by weight relative to the total weight of the tie.